1. Field of the Invention
The present invention relates to an optical sensor suitable for identifying a target in question and an image forming device incorporating such an optical sensor.
2. Description of the Related Art
An image forming device such as a digital copier or laser printer transfers a toner image onto the surface of a recording medium including a print paper, applies heat and pressure under a certain condition to fuse it, and forms an image. A heat amount and a pressure amount at the fusing need to be taken into account for forming an image. Particularly, to form high-quality images, a fusing condition needs to be set individually for kinds of recording medium.
This is because the quality of image is greatly affected by the material, thickness, moisture, smoothness, and coating of a recording medium. For example, in terms of smoothness, a toner fixation rate on the depressed portion of a print paper decreases depending on a fusing condition. Color unevenness in an image may occur unless an image is fused under a proper condition according to a recording medium.
Further, along with a progress of image forming devices and diversified representations, the types of recording media are various and there are more than several hundred different kinds of print papers. Moreover, in each kind of paper a variety of brands with different thicknesses and basis weights are available. It is necessary to set a detailed fusing condition for each brand of paper in order to generate high-quality images.
There has been an increase in the number of brands of plain paper, coated paper such as gross coated paper, matt coated paper, and art coated paper, plastic sheet, and special paper having an embossed surface.
Currently, users have to set a fusing condition of an image forming device in printing. Users are required to have knowledge to recognize different types of paper and it is troublesome for them to input settings for a kind of a paper in use. Optimal images cannot be acquired if there is an error in the settings.
An optical method in which a light is irradiated to a recording medium to detect a brand of the recording medium or a state of the surface thereof from a reflective or transmissive light beam by the recording medium is known.
For example, Japanese Patent Application Publication No. 2005-156380 (Reference 1) discloses a determining device to determine a kind of a recording medium using reflective and transmissive lights.
Japanese Patent No. 3362360 (Reference 2) discloses a printer having a determiner to separate an S-polarization component and a P-polarization component from a reflected light by a document to electrically determine a kind, presence or absence, or state of the surface of the document.
Japanese Patent Application Publication No. 2012-127937 (Reference 3) discloses an optical sensor to specify a brand of a paper from a light amount of P-polarization components of an internal diffuse reflection of light and that of S-polarization components of a surface specular reflection of light.
Japanese Patent No. 3830267 (Reference 4) discloses a surface inspection device which detects a roughness of a specimen surface from a reflected intensity of S-polarization components and that of P-polarization components.
However, it is hard to accurately specify an object in question.